Many project that use pytest for testing won't need to redefine it over
and over again in their .nxdtest file.

It is very handy to debug both .nxdtest and nxdtest tool itself, and to
be able to run tests locally during development instead of (in addition
to) waiting for the test result from test nodes.

-> Teach nxdtest to run and report tests locally if no --master_url was
provided.

Idea is taken from runTestSuite.in from NEO, Cython+, Buildout and Rina:

https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L95-105
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L55-75
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/stress-testing/runTestSuite.in#L17-37
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/cython-test/runTestSuite.in#L38-58
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/buildout-testing/runTestSuite.in#L21-39
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/build-rina/runTestSuite.in#L29-49

Instead of copying code over and over again, let's stick to UNIX
approach and make it to be in one tool only that does its job
(hopefully) good.

Previously, if --master_url was not provided, the program would crash
with UnboundLocalError for status, since for that case list of tests was
empty. Fix it by moving status initialization higher by one level.

See next patch where we'll add meaning for nxdtest run with no
--master_url set.

It is frequently needed to set some environment variable without
completely resetting everything else in the environment, because that
everything else can carry settings like PATH, PYTHONPATH, RPATH, etc for
the program to be able to run at all.

See pygolang@b938af8b for recent example.

After previous patch that summary function is no-longer used, is
specific to NEO/py and so should be defined in .nxdtest file in that
project. lab.nexedi.com/kirr/neo will be adjusted correspondingly.

Make the tool generic: load list of testcases to run from .nxdtest file
and process the correspondingly. See added top-level documentation for
details.

Amends e9cc7e07 (Add minimal packaging setup)

So that nxdtest could be installed as egg via pip or buildout.

We will use it as the base for nxdtest.
Original history:

kirr/neo@51b18490
kirr/neo@f67c147d
kirr/neo@0e28fbb8

We send output from tested process to master. We also print it to
stdout,stderr so it appears in testnode logs.

However till now it was like, whole output first read, and only then
emitted to log as a whole, thus not allowing to oversee current test
progress by watching testnode log tail.

Fix it by implementing the teeing process manually.

Some draft history related to this patch:

	lab.nexedi.com/kirr/neo/commit/aa370ca3        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/096550b1        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/63956f43        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/b9819d0e        X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally

The wrapper runs `neotest bench-local` in neotest SlapOS instance:

	https://lab.nexedi.com/nexedi/slapos/blob/ab8705f4/software/neotest/instance.cfg.in

Extracted from slapos!282

Nxdtest is conceived as a tox-like tool to run tests for a project under
Nexedi testing infrastructure.